The present invention relates to an inflatable vehicle passenger restraint system that momentarily restrains an occupant during the critical instant of an impact. More particularly, the present invention relates to such a system incorporating dual air bags, where an inner air bag is located within an outer air bag.
Inflatable restraint systems have become commonplace for passenger protection. Current federal regulations require all automobiles manufactured within the United States to be equipped with a passive restraint system, either an inflatable restraint system such as an air bag or a passive seat belt.
A typical inflatable restraint system includes three basic components: a crash sensing mechanism which mounts to the vehicle frame, an air bag assembly located within the passenger compartment and a gas generator to deploy and inflate the air bag. In operation, the air bag is inflated before there is appreciable vehicle--occupant interaction. The air bag must have sufficient capacity to arrest the forward motion of the occupant relative to the vehicle interior without allowing the occupant to penetrate through the air bag and impact the underlying vehicle structure.
While single bag construction remains the predominant approach, inflatable occupant restraint systems incorporating multiple air bags have been proposed in the prior art. For example, a typical arrangement having multiple air bags inflates a first air bag to envelope the occupant and a second air bag which functions as a knee bolster is disclosed in U.S. Pat. No. 4,360,223 issued to Kirchoff.
None of the prior art, however, is without its problems. The biggest problem inherent in traditional inflatable restraint systems is a lack of flexibility to adequately provide protection for occupants of a vehicle other than the driver. The difficulty in protecting passengers other than the driver is the potential of those passengers being "out of position." Passengers other than the driver are not as constrained as to how or where they position themselves within the vehicle. Most danger to the "out of position" occupant occurs when they are located in a position forward of a seated position and, therefore, contact the bag while it is still rapidly expanding.
Inflatable restraint systems are designed to deploy and inflate during the time interval between the initial sensing of the impact by a crash sensing mechanism and the resulting forward movement of the occupant relative to the vehicle. Because this time interval lasts only milliseconds, the air bag must inflate with a tremendous flow rate of gas. This tremendous flow rate produces what is referred to as a "hard fill". This "hard fill" can be likened to a small explosion that is contained by the air bag.
Ideally, the forces produced during inflation are entirely self-contained by the air bag through its full expansion before the occupant comes in contact with the air bag. Should the occupant be improperly seated, or "put of position", the impact of the explosion may be partially absorbed by the occupant. As a result, the occupant may suffer injury from the expansion process as well as the accident.
The present invention provides an inflatable restraint system in which the air bag which restrains the occupant is inflated at a softer fill rate, thereby minimizing injury resulting from the rapid inflation of the air bag. The present invention also provides an inflatable restraint system suitable for after-market application.